Department of Biological Sciences, Old Dominion University, Norfolk, VA, 23529, USA.
Office of Biological and Environmental Research, US Department of Energy, Washington, DC, 20585, USA.
New Phytol. 2013 Nov;200(3):778-787. doi: 10.1111/nph.12246. Epub 2013 Mar 25.
Uncertainty surrounds belowground plant responses to rising atmospheric CO₂ because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability. We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11 yr of elevated atmospheric CO₂ using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using ground-penetrating radar and total root biomass using soil cores. Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO₂ occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes. Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO₂. Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO₂. The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO₂ enrichment.
由于根系动态变化较快，需要频繁监测，而资源供应敏感性又导致需要长期监测，因此，地下植物对大气中 CO₂ 升高的反应存在不确定性。我们利用开顶式气室，报告了佛罗里达州栎灌丛生态系统在 11 年大气 CO₂ 升高下的地下植物反应。我们利用微根管测量了细根的生产、周转率和生物量，利用探地雷达测量了粗根的生物量，利用土壤芯测量了总根的生物量。在高 CO₂ 条件下，总根生物量大于对照条件下，且绝对差异大于地上部分。细根生物量波动幅度超过两倍，没有单向时间趋势，而叶片生物量则单调增加。在火灾和飓风干扰后，细根生物量随着 CO₂ 升高而显著增加。叶片生物量在飓风后也表现出更强的响应。火灾和飓风后的响应表明，干扰促进了植物对 CO₂ 升高的生长响应。干扰带来的资源可用性增加（养分、水、空间）可能会促进根系对 CO₂ 升高的更大响应。细根响应的消失表明根系系统对 CO₂ 富集的响应能力存在限制。
